1,721,056 research outputs found
Zircon geochronology of Archaean felsic sequences in the Zimbabwe craton: a revision of greenstone stratigraphy and a model for crustal growth
No full textU-Pb ion-microprobe (SHRIMP) work on zircon populations from 13 Zimbabwean Archaean felsic rocks are presented and interpreted. Samples were extracted from felsic volcanic sequences from most of the major greenstone belts and represent the first zircon geochronological data from within the greenstone belts themselves. The data demonstrate a Late Archaean volcanicity spanning 250 Ma which began at least 2900 Ma ago and ended at 2650 Ma. Theintrusion of extensive granitoid sills of the Chilimanzi suite at c. 2.6 Ga marks the widespread stabilization of the craton. Based on the new zircon data and a re-evaluation of published mapping, a new stratigraphic subdivision is presented for the Late (< 2.9 Ga) Archaean of Zimbabwe. A feature of the stratigraphic model is the cyclicity of magmatism which begins with ultramafic-mafic rocks, progresses through felsic volcanism and ends with a granitoid event. These cycles are repeated at least three or four times in the 250 Ma time span. An important characteristic of the felsic volcanic rocks is that the bulk of the material examined contains inherited, xenocrystic zircons whose ages range from 1000 Ma to 20 Ma older than the host rocks. The oldest xenocrystic zircons (c. 3.6 Ga) are restricted to volcanic rocks which erupted through the Tokwe segment; itself the only known > 3.3 Ga fragment of Archaean crust in Zimbabwe. These data suggest that the Early Archaean crust is restricted to the Tokwe segment in the south of the country. Since even the oldest of the felsic volcanics (2.90 Ga, Lower Belingwean) have zircons which are 50 Ma older, it is suggested that remnants of earlier cyclic greenstone--granitoid events must underlie the present craton and that all of the currently exposed greenstone belts of Zimbabwe were developed on sialic crust
Geochronological record of plutonic activity on a long-lived active continental margin, with emphasis on the pre-Andean rocks of Chile
No full textFil: Calderón, M.. No especifíca;Fil: Hervé, Francisco. No especifíca;Fil: Munizaga, Francisco. No especifíca;Fil: Pankhurst, R.J. No especifíca;Fil: Fanning, C.M. No especifíca;Fil: Rapela, Carlos Washington. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentin
U-Pb dating of stockwork zircons from the eastern Iberian Pyrite Belt
No full textZircons found in the stockwork zones of the massive sulphide Los Frailes deposit, Iberian Pyrite Belt, are interpreted to have grown during the hydro-thermal alteration of host felsic volcanic rocks. Ion microprobe (SHRIMP) dating gives a206Pb/238 U age of 345.7 ± 4.6 Ma (2?) and together with published spore data from the deposit suggest an age of uppermost Devonian to lowermost Carboniferous. Stockwork zircons offer the possibility of precisely defining the emplacement ages of these giant sulphide accumulations over the whole Pyrite Belt and from this will emerge estimates of the thermal budget necessary to generate the deposits
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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